1. Field of the Invention
This invention concerns a numerical control device, particularly a numerical control device for multi-system-controlled machine tools, which is capable of maintaining a relationship among particular positions in the systems even when speed override is applied, thereby safeguarding against interaction between machines.
2. Description of the Background Art
FIG. 6A is a block diagram which illustrates the composition of a multi-system numerical control device. In this figure, 1a and 1b represent the tape, 2a and 2b the program analysis means, 3a and 3b the interpolation means, 4a and 4b the acceleration/deceleration means, 5a and 5b the drive section, 6a and 6b the motor, 7 the speed override device, and 8a and 8b the speed calculating means. The acceleration/deceleration means 4a and 4b may have a design as disclosed in U.S. Pat. No. 4,554,497, or similar designs known in the art. In the same figure, 10a represents the group of devices for system 1 comprising 1a, 2a, 3a, 4a, 5a, 6a and 8a while 10b represents the group of devices for system 2 comprising 1b, 2b, 3b, 4b, 5b, 6b and 8b.
The operation of these parts is now described briefly using FIG. 6B, which is a flowchart which shows the acceleration/deceleration processing operations known in the art. First, at step S1 punched tapes 1a and 1b containing the machining program in NC language are analyzed by program analysis means 2a and 2b, and at step S2 it is determined as to whether there is a speed override command from speed override device 7. If it is determined that there is a speed override command, the speed with the speed override applied is calculated by speed calculating means 8a and 8b at step S3, and at step S4 interpolation processing is provided by interpolation means 3a and 3b. If it is determined at step S3 that there is no speed override command, the interpolation processing is provided as is at step S4. Based on the data yielded by the interpolation processing, at step S7 the acceleration/deceleration is provided by acceleration/deceleration means 4a and 4b for a prescribed period of time, and thus motors 6a and 6b are driven and controlled through drive sections 5a and 5b, respectively. The machine's time constant common to all the systems is determined in line with the system having the highest time constant.
FIGS. 7A and 7B comprise a series of graphs showing the acceleration/deceleration patterns created by acceleration/deceleration means 4a and 4b, and in these graphs the vertical axis represents the transfer rate and the horizontal axis the time. In FIG. 7A, graph 71a shows the acceleration/deceleration pattern when speed override is not applied to axis X1 of system 1, with "F" denoting the feedrate, "J" the time constant, "T01" the transfer time, and "L1" the transfer distance. In FIG. 7B, graph 72a shows the acceleration/deceleration pattern when speed override is not applied to the X2 axis of system 2, with "F" denoting the feedrate, "J" the time constant, "T02" the transfer time, and "L2" the transfer distance. When speed override is not applied, transfer finish time "T01" of system 1 is represented by formula (1) given below, and transfer finish time "T02" of system 2 is represented by formula (2) given below. These formulae apply when the speed and time constants of the first and second systems are equal. EQU T01=L1/F+J (1) EQU T02=L2/F+J (2)
FIG. 8A is a graph showing the relationship between the positions of axis X1 in system 1 and axis X2 in system 2 with an acceleration/deceleration pattern such as that in graphs 71a and 72b of FIGS. 7A and 7B. The vertical axis represents the position and the horizontal axis the time. 81a indicates axis X1 in system 1, and 82a axis X2 in system 2. When, for instance, axis X1 is at position A1 at time T01, axis X2 will be at position A2 at the same moment.
In order to reduce the time for machining work to the minimum and enhance efficiency of the machining, programs are prepared to move the machines in each system with minimal waste in movement and to avoid machines coming into contact with each other by properly arranging the timings between the systems concerned. To ascertain whether a program actually produces the intended movements, work is cut on a trial basis, and adjustments are then made to the program. However, if the machines are made to move at the actual machining speeds, these speeds are so fast that it is hard to check the movements. Furthermore, due to the high speed of the machines, mistakes made in the program stand the risk of resulting in contact between machines or tool breakage.
This is why programs are normally checked by applying speed override to slow down the machine speeds. At slower speeds, it becomes possible to stop the machines in time if it appears that the machines will collide, and also to visually check their movements easily because they are moving slowly. Speed override is applied in such cases with conventional multi-system numerical control devices. As an example of this feature, a speed override of 50% is applied to the acceleration/deceleration pattern shown in graphs 71a and 72a of FIGS. 7A and 7B. The override is applied only to the speed, i.e., the height of the current on the vertical axis is changed as is the length of the wave along the time axis, but it does not affect the acceleration (angle of increase) or deceleration (angle of decrease) of the wave. The resulting finish times TN1 for system 1 and TN2 for system 2 are represented by formulae (3) and (4), respectively; and the resulting acceleration/deceleration patterns are shown in 71b of FIG. 7C for axis X1 of system 1 and in 72b of FIG. 7D for axis X2 of system 2. EQU TN1=2L1/F+J (3) EQU TN2=2L2/F+J (4)
FIG. 8B is a graph showing the relationship between the positions of axes X1 and X2 of systems 1 and 2 when the override in 71b and 72b of FIGS. 7C and 7D has been applied. The vertical axis represents the position and the horizontal axis the time; 81b shows axis X1 of system 1 and 82b axis X2 of system 2. When axis X1 is at position A1 at time TN1, axis X2 is in actual fact at position B2 although it should be at position A2. Thus, the relationship between the positions in the systems is lost.
Considered next is an instance where the speeds are different. FIGS. 9A-9D comprise a series of graphs showing the acceleration/deceleration patterns created by acceleration/deceleration means 4a and 4b, and in these graphs the vertical axis represents the transfer rate and the horizontal axis represents the time. In FIG. 9A, graph 91a shows the acceleration/deceleration pattern when speed override is not applied in system 1, with "F1" denoting the feedrate, "J" the time constant, "T01" the transfer time, and "L1" the transfer distance. In FIG. 9B, graph 92a shows the acceleration/deceleration pattern when speed override is not applied in system 2 which has a different speed from system 1, with "F2" denoting the feedrate, "J" the time constant, "T02" the transfer time, and "L2" the transfer distance. When speed override is not applied, transfer finish time "T01" of system 1 is represented by formula (5) given below, and transfer finish time "T02" of system 2 is represented by formula (6) given below. FIG. 10A is a graph showing the relationship between the positions of axis X1 in system 1 and axis X2 in system 2 with an acceleration/deceleration pattern such as that in graphs 91a and 92a of FIGS. 9A and 9B. The vertical axis represents the position and the horizontal axis the time. 101a indicates axis X1 in system 1, and 102a axis X2 in system 2. When, for instance, axis X1 is at position A1 at time TN1, axis X2 will be at position A2. EQU T01=L1/F1+J (5) EQU T02=L2/F2+J (6)
As an example of a difficulty that may arise with the conventional case, consider now a situation in which the speed override (R) is 50%. Graph 91b of FIG. 9C shows the acceleration/deceleration pattern that results when a 50% (normally 0.ltoreq.R.ltoreq.1) speed override is applied to the above-mentioned numerical control device system 1; graph 92b of FIG. 9D shows the acceleration/deceleration pattern applying when a 50% speed override is applied to the above-mentioned numerical control device system 2. Transfer finish time "TN1" of system 1 is represented by formula (7) given below, and transfer finish time "TN2" of system 2 is represented by formula (8) given below. FIG. 10B is a graph showing the relationship between the positions of axis X1 in system 1 and axis X2 in system 2 when override as shown in graphs 91b and 92b in FIGS. 9C and 9D is applied. The vertical axis represents the position and the horizontal axis the time. 101b indicates axis X1 in system 1, and 102a axis X2 in system 2. When axis X1 is at position A1 at time TN1, axis X2 is in actual fact at position B2 although it should be at position A2, and the relationship between the positions in the systems is thus lost. EQU TN1=2L/F+J1=2T01-J1 (7) EQU TN2=2L/F+J2=2T02-J2 (8)
The time constants of a machine are calculated in accordance with the capacity and characteristics of that machine, and the lowest possible time constants within the allowable range are used. In a conventional multi-system numerical control device such as that described above, the time constant of the system with the highest time constant among all the systems was used as the time constant common to all the systems. However, in order to further reduce the machining time and raise efficiency, it is better to use the lowest time constant for each system rather than one time constant which is common to all the systems.
FIGS. 11A-11D comprise a series of graphs showing the acceleration/deceleration patterns created by acceleration/deceleration means 4a and 4b, and the time constants differ for systems 1 and 2. In these graphs, the vertical axis represents the transfer rate and the horizontal axis represents the time. In FIG. 11A, graph 111a shows the acceleration/deceleration pattern when speed override is not applied in system 1, with "F" denoting the feedrate, "J1" the time constant, "T01" the transfer time, and "L1" the transfer distance. Note that the feed ratio for both axis is the same. In FIG. 11B, graph 112a shows the acceleration/deceleration pattern when speed override is not applied in system 2 with a different time constant from that of system 1, with "F" denoting the feedrate, "J2" the time constant, "T02" the transfer time, and "L2" the transfer distance. Again the feed ratio for both axis is the same. When speed override is not applied, transfer finish time "T01" of system 1 is represented by formula (9) given below, and transfer finish time "T02" of system 2 is represented by formula (10) given below. EQU T01=L/F+J1 (9) EQU T02=L/F+J2 (10)
FIG. 12A is a graph showing the relationship between the positions of axis X1 in system 1 and axis X2 in system 2 with an acceleration/deceleration pattern such as that in graphs 111a and 112a of FIGS. 11A and 11B. The vertical axis represents the position and the horizontal axis the time. 121a indicates axis X1 in system 1, and 122a indicates axis X2 in system 2. When, for instance, axis X1 is at position A1 at time T01, axis X2 will be at position A2.
As an example of a difficulty arising in the conventional case, consider now a situation where the speed override is 50%. Graph 112b of FIG. 11C shows the acceleration/deceleration pattern applying when a 50% (normally 0.ltoreq.R.ltoreq.1) speed override is applied to the above-mentioned numerical control device system 1. Graph 111b of FIG. 11D shows the acceleration/deceleration pattern applying when a 50% speed override is applied to the above-mentioned numerical control device system 2. Transfer finish time "TN1" of system 1 is represented by formula (11) given below, and transfer finish time "TN2" of system 2 is represented by formula (12) given below. EQU TN1=2L1/F+J1=2T01-J1 (11)
TN2=2L2/F+J2=2T02-J2 (12)
FIG. 12B is a graph showing the relationship between the positions of axis X1 in system 1 and axis X2 in system 2 when override as shown in graphs 111b and 112b in FIGS. 11C and 11D is applied. The vertical axis represents the position and the horizontal axis represents the time. 121b indicates axis X1 in system 1, and 122b indicates axis X2 in system 2. When axis X1 is at position A1 at time TN1, axis X2 is in actual fact at position B2 although it should be at position A2. Thus, the relationship between the positions in the systems is lost.
Indicated below are the problems which arise when the relationship between the positions in the systems is lost, as mentioned above.
Consider the multi-system lathe such as that shown in FIG. 13. In the figure, 131 and 133 represent the tool rests, 132 and 134 the cutting tools mounted on tool rests 131 and 133, respectively, 135 the work, and 136 the spindle that turns work 135. Tool rest 131 is moved along the X1 axis, and tool rest 133 along the X2 axis. Spindle 136 moves along the Z1 axis. System 1 is composed of tool rest 131 and spindle 136; system 2 is composed of tool rest 133 and spindle 136. 137 is the coordinate system of system 1 and system 2 the coordinate system of 138. The operations of the machine are now described using the two illustrations of FIG. 14A and 14B.
In these figures, as shown in FIG. 14A, tool rest 131 moves along the X1 axis of system 1, and work 135 is cut as far as X11 along the system 1 X1 axis by moving spindle 136 along the Z1 axis. Next, as shown in FIG. 14B, in order to save the time for synchronization, systems 1 and 2 are efficiently moved, and as soon as the cutting of the work is finished, tool rest 133 is moved as far as X11 along the system 2 X2 axis, and the work is machined as far as X21. A case where the relationship between the positions in the systems is lost by applying speed override in a multi-system lathe such as the one described above will now be outlined using the two illustrations of FIG. 15A and 15B.
Originally, tool rest 133 should move as far as X11 along the system 2 X2 axis after having cut as far as X11 along the system 1 X1 axis in FIG. 15A. However, by applying speed override, the synchronization between the systems is lost and, regardless of the fact that cutter 131 of system 1 is still cutting work 135 which has not been cut as far as X11, tool rest 133 of system 2 is about to move as far as X11 along system 2 axis X2. As a result, tool rest 133 and work 135 make contact, as shown in FIG. 15B, and there is a risk that the tool will break.
In this way, therefore, when speed override is applied to a conventional multi-system numerical control device, if the axis transfer rates differ between systems and/or if the acceleration/deceleration means have different time constants for each system, the position relationship between the systems will be lost, and problems will arise in the risk of tool breakages or contact between machines.